The subject matter disclosed herein relates to turbines and, in particular, to management of compressor and turbine airfoil lifetimes.
A gas turbine engine typically includes a compressor, a combustor, and a turbine. The compressor and turbine generally include rows of airfoils or blades that are axially stacked in stages. Each stage generally includes a row of circumferentially spaced stator vanes, which are fixed, and a set of circumferentially spaced rotor blades, that rotate about a central axis or shaft. Generally, in operation, the rotor blades in the compressor rotor rotate about the shaft to compress a flow of air. The supply of compressed air is used in the combustor to combust a supply of fuel. The resulting flow of hot gases from the combustion is expanded through the turbine, which causes the turbine rotor blades to rotate about the shaft. In this manner, the energy contained in the fuel is converted into the mechanical energy of the rotating blades, which may be used to rotate the rotor blades of the compressor and the coils of a generator to generate electricity. During operation, because of the extreme temperatures, the velocity of the working fluid, and the rotational velocity of the rotor blades, the stator vanes and the rotor blades, through both the compressor and the turbine, are highly stressed parts.
Often, in both the compressor and the turbine sections of the turbine engine, rows of stator vanes of nearby or neighboring stages are configured with substantially the same number of circumferentially spaced vanes. In an effort to improve the aero-efficiency of turbine engines, efforts have been made to index or “clock” the relative circumferential positions of the airfoils in one row to the circumferential position of the airfoils in nearby or neighboring rows. However, while only minimally or negligibly improving engine aero-efficiency, it has been discovered that such conventional clocking methods generally function to increase the mechanical stresses acting on airfoils during operation. Of course, increased operational stresses can cause airfoils rocking and, ultimately, failures, which may result in extensive damage to the gas turbine engine.
High availability and reliability of power generation systems has been a major requisite of the electric utility industry for many years. The high cost of unreliability and forced outages is well known. Improper maintenance or operational anomoly detection may lead to turbine-forced outages. Early detection of such anomolies is important in preventing and reducing lengthy turbine forced outages.
A typical inspection may require that a turbine be shut down during the inspection. In such a case, at least a portion of a power generation plant's production capability may be hampered. Reducing the ability to generate power may have real economic costs associated with it. In addition, the inspection itself costs money. For at least these two reasons, it may be beneficial to perform inspections only when needed.